The present invention relates to a tray-type elevator conveyor and, more particularly, a tray-type elevator conveyor for a rack or cabinet with paternoster-type load carriers which are suspended from radially outward projecting joints of straddle levers and passed over rotating bodies by means of at least one endless chain or the like, the straddle levers being so dimensioned with respect to the rotating bodies as to adjust the distance between the suspension points and the chain so that this distance will be smaller on the end rounding portions than it is on the straight runs.
It is the object of this invention to provide a tray-type elevator conveyor wherein the speed difference between the straight runs and the curved portions of the orbital path is reduced and which affords an optimum utilization of the available space combined with a free choice and spacing of the load carriers, initially as well as subsequently.
Generally, the load carriers are so guided on their orbital path by means of carrying arms projecting from the chain as to permit a relatively close succession on the straight run and avoid obstruction of the circulating motion when rounding the conveyor ends on the curved portions of the path. This is accomplished at the expense of unnecessarily large clearances on the curved portions of the orbital path. Furthermore, the traveling speed in the direction of conveyance is suddenly increased or reduced at the start and termination of the end rounding motion.
The resulting nonsteady movements may cause undesirable oscillations of the load carriers. To avoid this, it has been suggested heretofore -- in West German Utility Pat. No. 1,866,533 -- to use carrying arms in the form of straddle levers consisting essentially of individual levers which are pivoted on the chain and provided with a central joint whose pivot also serves as supporting pivot for suspending the load carriers. A further requirement is that the length of the unequally long individual levers be approximately equal to the diameter of the rotating rollers and that the individual levers of each carrying arm be spaced apart by a distance corresponding to about half the circumference of the deflector rollers. What is achieved thereby is that the distance between the suspension points of successive load carriers is smaller on the curved portion of the orbital path than it is on the straight run so that owing to the reduced length of the carrying arm during the end rounding movement the mass acceleration forces are lower than they would be with a carrying arm of unchanging length.
While the suspension points on fixed carrying arms describe a circular arc during the end rounding movement, i.e. when they are transferred from the ascending to the descending run or vice versa, the curved portions of the path obtained with variable carrying arms of the type described have the form of a pointed parabola with non-steady speeds on the end rounding portion of the path which, although reduced as compared with those caused by movement along a circular arc (with fixed carrying arms), still feature very high levels of normal and tangential inertia forces.
This has a particularly adverse effect during starting and braking. The result is increased wear and the need for comparatively elaborate and expensive drive means. Furthermore, severe limitations are imposed upon the traveling speed of the load carriers on the straight runs inasmuch as the system tends to oscillate on the curved portions of the path and, moreover, the load may easily slip out of the load carriers during starting and braking.
For all these reasons, the traveling speed is limited. However, this limitation is irreconcilable with the requirement that tray-type elevator conveyors should afford quick access and, consequently, move the load carriers at maximum possible speed.
Furthermore, the known tray-type elevator conveyors do not permit the simultaneous use of load carriers of different sizes or weights without a substantial loss of space, nor can the spacing and/or dimensions of the load carriers be changed subsequently without a loss of space, especially in the case of tray-type elevators with stabilizing guide means.